By Bruce Rottink, Volunteer Nature Guide
Originally posted in August of 2013, this Naturalist Note was among several that were lost due to a computer glitch in early 2014. I’m re-posting so it isn’t lost forever!
Months ahead of Halloween, Tryon Creek State Natural Area is already swamped with skeletons! They’re everywhere! But these skeletons aren’t the bony remains of dead animals; they’re the nearly invisible outlines of dead tree leaves. At a time when the red alder (Alnus rubra) leaves should look like this:
Many look like this:
The red alder trees in the park and beyond are under attack by an outbreak of the alder flea beetle (Macrohaltica ambiens), a species native to the United States. The tiny black larvae of this beetle are the main culprits. These ¼-inch long gluttons hatch in late spring and start feeding. They only eat the soft parts of the leaf, leaving a leaf skeleton that consists of the tougher leaf veins. Under normal circumstances, these veins carry water from the roots up to the leaves. These veins also transport the sugars produced by photosynthesis in the leaf to nourish other parts of the plant like the trunk and roots. The close-up below shows the tree’s finely detailed plumbing system.
As devastating as the attack is, one can’t help but find some lacey beauty in these skeletonized leaves.
About early August, the larvae drop to the ground and pupate. After the 10-day pupation period, they emerge as adult beetles. As if the larvae hadn’t done enough damage already, the adult beetles then attack more alder leaves. They chew holes in the leaves, as seen in the following photo. Finally, the adults drop down into the debris on the forest floor and hibernate until spring. In the spring, the adults emerge, mate, and the cycle starts all over again.
The alder leaf beetle primarily attacks alders, but will sometimes feed on other trees like willows (Salix spp.) and poplars (Populus spp.). However, at Tryon Creek this year, it looks like the damage is confined to alders. This beetle is just one of a number of insects that “skeletonize” leaves of different plants.
Arborists have indicated that the alders will survive; no need to panic on that score. On the other hand, alder leaves normally stay green on the trees until quite late in the autumn. The beetle is robbing the trees of the opportunity to photosynthesize for a couple of extra months. The carbohydrates that the tree would normally create and store during this period will be missing! With lower food reserves in the spring, the tree’s growth will probably be reduced next year.
Expert opinion is that vigorous trees are less likely to be attacked. The beetles focus on vulnerable trees that are water stressed or otherwise in poor health. The number of beetles present in the forest varies dramatically from year to year. Perhaps this year’s outbreak is related to the extended dry period we are experiencing.
There is a lesson here related to global warming. Some trees will die because the climate gets too hot or too dry for them to survive. But in many cases, scientists have already found that climate change will stress the trees, and then the opportunistic insects and diseases which attack unhealthy trees will be death’s deliverymen.
By Bruce Rottink, Volunteer Nature Guide & Retired Research Forester
This article was originally written and posted in 2013, but vanished from the website during a computer crash in early 2014.
Most people come to Tryon Creek State Natural Area because of all the wonderful things they know they’ll find: majestic Douglas-firs, beautiful flowers and lots of birds. But sometimes, nature has surprises in store, which can both amaze and delight us.
One such amazing surprise is a large living Douglas-fir stump in the northern part of the park. A “living stump” sounds like a contradiction. The leaves or needles in the crown of the tree produce all of the tree’s food. Thus, you would think that once a tree is cut down, the stump is finished, dead, history. Mostly, that’s true, but that is not always the case.
What allows a stump to stay alive after the trunk and crown are removed? Root grafts! Unseen by human eyes, many trees form natural root grafts with other nearby trees of the same species.
Scientists have learned over the years that both water and nutrients can flow through these natural root grafts. If two trees are root grafted together, and one is cut down, enough water and nutrients can flow from the standing tree to the stump to keep the stump alive for many years. The response of the living stump is to try to heal over the cut surface where the trunk was severed.
The most common type of root grafting is between two roots of the same tree. Next most common is between two different trees of the same species. Root grafts between trees of two different species have been found, but they are extremely rare, and mostly occur between two species that are able to hybridize with each other.
Most often, a healing callus, which looks like a kind of scab, starts from the edge of the cut stump, and gradually grows towards the center of the stump. This callus is produced by the tree’s cambium which is a thin layer of actively dividing cells between the bark and the wood of the tree. This is a very slow process. In rare cases, this callus eventually caps the entire stump.
I found an impressive living Douglas-fir stump at TCSNA. The probable root graft partner of this particular living stump is a large Douglas-fir tree growing less than 6 feet away. The newly discovered living stump at Tryon Creek is remarkable on two counts. First, it is huge. The circumference of the stump is 9 feet, 4-1/2 inches. Secondly, the cut surface on the top of the stump is completely healed over. The red lines I’ve added indicate the top of the original stump. In all my 10 years of experience as a Research Forester, I have never seen a stump even close to this size that was completely healed.
As cool as this root grafting and living stump phenomenon is, this is not necessarily a positive thing for the trees. One of the best documented problems is that tree diseases are readily transmitted from tree to tree through these root grafts. The most famous example of tree diseases spreading through root grafts is Dutch elm disease that has devastated urban street trees in the eastern U. S. In Douglas-fir, diseases such as laminated root rot (Poria weirii) can also be transmitted from tree to tree via the root grafts.
If you would like to see one of Tryon Creek State Natural Area’s living stumps, it’s easy. There is a great example of a living stump near High Bridge. Starting at High Bridge, take the short (0.04 miles) trail leading to the North Horse Loop. At the junction of this short trail, and the North Horse Loop, look to the southeastern side of the trail, and there is a living stump, which is circled in red below:
What other oddities are there in the park? Next time you visit, keep a sharp lookout for strange things, and maybe you can discover Tryon Creek’s next natural wonder!
Spiders and Their Webs
By Bruce Rottink, Volunteer Nature Guide & Retired Research Forester1
Note: This is my 61st Naturalist Note. If you are interested in reading about a special topic, enter that topic in the blank space with the magnifying glass in the upper right hand corner of the Naturalist Notes webpage and click on “GO.”
Many species of spiders spin webs to trap their food. These webs are elaborate constructions of both sticky and non-sticky strands of silk composed of proteins. In many cases, the spiders will eat their webs each day, and create a new one either overnight, or in the morning. Published estimates on how long it takes to construct a web vary from about 15 minutes to an hour.
Spiders use the webs to trap insects for food. The spiders are depending upon the fact that the insects typically do not see their webs, and fly right into them and get caught. The invisibility of the web is important. Therefore, if some “trash” gets caught in the web, it seriously elevates the visibility of the web. In at least some cases, the spiders expend the effort needed to remove the “trash” and keep their webs clean. This web-cleaning is not always an easy process, but if it maintains the invisibility of the web, it can be very important.
I made the below video at Tryon Creek State Natural Area. I started the process by tossing a small piece of a maple leaf into the spider’s web. In order to maintain the “invisibility” of the web, the spider decided to clean the piece of maple leaf out of its web. The spider does it very skillfully, and then repairs at least a small part of the web. During the web repair, you can see the spider using one of its hind legs to pull the silk strand out of its rear end.
I would encourage you to watch this video to satisfy your curiosity about how spiders clean their webs. Spiders spend a lot of effort building their webs to trap their prey. Cleaning their web also takes a lot of effort, and often leaves the web in worse condition. So please avoid throwing stuff into a spider’s web at your house, or at the Park. Having “stuff” in their web makes the spider’s life more difficult. The spiders will appreciate your restraint.
In the video there are some sections which are not in perfect focus, in part because the spider web is moving back and forth. However, you will be able to easily see the work of the spider.
1Thanks to Roland Begin and Deb Hill for their review and suggestions on this Naturalist Note.